In High Dynamic Range (HDR) video, contrast steps between consecutive coded levels are generally increased in comparison to Standard Dynamic Range (SDR) video because a larger range of luminance has to be coded with nearly the same number of quantized levels. Resultantly, this may produce some visual artifacts such as contouring or banding, especially in areas showing a low-contrast gradient. These visual artifacts may be avoided by adding some noise in the problematic areas so as to emulate a smoother video signal; dithering being one of the most common methods used to generate such noise by randomizing the quantization error. However, the current video compression algorithms implemented by common, standard codecs are unable to preserve such a noisy signal unless the bit rate is increased far beyond the admissible limits of common use cases.
Therefore it is the object of the present invention to introduce a method for processing HDR video in order to improve the perceived visual quality of encoded content. The present invention proposes to use an encoder to compute a residual image at the same, full bit depth as an original image that is to be compressed, as opposed to computing the residual image at a reduced bit depth. Furthermore, a contrast analysis is performed on the original image in order to detect potential problematic areas when compressing the original image. The contrast analysis is utilized to compute a plurality of quantizers that is utilized to allocate more bandwidth to the potential problematic areas when forming a quantized image. The encoder inserts high frequency components into the quantized image in order to preserve accuracy when the compressed image is decoded. applied to the frequency signal in order to produce a quantized image. The plurality of quantized coefficients is applied to a plurality of frequency components of the frequency signal in order to produce a reduced frequency signal (a quantized image). The encoder then inserts high frequency components into the reduced frequency signal, wherein a compressed image is encoded using the reduced frequency signal and the predicted image.